1. Field of the Invention
This invention relates to an inter-network connection apparatus for connecting networks such as LANs (Local Area Networks) to relay frames.
2. Description of the Related Art
There is an MAC (Media Access Control) bridge apparatus as one typical inter-LAN connection apparatus.
FIG. 1 shows a conventional MAC bridge apparatus. As is shown in FIG. 1, an MAC bridge apparatus comprises LAN control sections 41-1-41-n, a bus/arbiter section 43, a frame buffer memory 44, a CPU (Central Processing Unit) 45 and a local memory 46. The MAC bridge apparatus connects the LAN control sections 41-1-41-n to the bus/arbiter section 43 via system interfaces 42-1-42-n, respectively. The LAN control sections 41-1-41-n commonly use, via the bus-artiber section 43, the frame buffer memory 44 for temporarily storing received frames.
The LAN control sections 41-1-41-n correspond to the physical layer and the data link MAC sub layer of an OSI (Open System Interconnection), and transmit a frame between each of LANs 5-1-5-n and the frame buffer memory 44. At the time of the transmission of a frame, the LAN control sections receive a request for frame transmission from the CPU 45 and output a signal thereto to notify the receipt of a frame.
The system interfaces 42-1-42-n write frame data into the frame buffer memory 44 via the bus/arbiter section 43, and read frame data from the frame buffer memory 44 to transmit it. An arbiter contained in the bus/arbiter section 43 arbitrates requests from the system interfaces 42-1-42-n and the CPU 45 for accessing the frame buffer memory (common memory) 44.
On the basis of programs stored in the local memory 46, the CPU 45 concentratedly controls (1) frame-filtering (frame-discharging) processing, (2) frame-relaying processing and (3) MAC address-learning processing, which are to be performed in the bridge apparatus of FIG. 1.
As described above, the conventional bridge apparatus employs a structure, in which the frame buffer memory for temporarily storing received frames is commonly connected, via the common bus, to the LAN control sections connected to respective LANs, and in which the CPU concentratedly controls bridge processing in response to that signal from each LAN control section which notifies the receipt of a frame.
Accordingly, the capability of the conventional bridge apparatus to relay frames depends upon the data transmission speed of the bus as a transmission path of frame data, also upon the performance of the arbiter (bus arbiter) for performing arbitration regarding bus access between each LAN control section and the CPU, and upon the performance of the CPU. In other words, these are some bottlenecks to enhance the capability of relaying frames.
On the other hand, in accordance with the spread of an FDDI (Fiber Distributed Data Interface) of a transmission speed of 100 Mbps, and with the development of a large-scaled LAN system, the transmission speed of each LAN and the number of the connections of LANs have been increased.
As a result, there is a demand for greatly enhancing the frame relay capability of the bridge apparatus.
In the conventional bridge apparatus, however, the frame relay capability depends upon the data transmission speed, the performance of the arbiter and the performance of the CPU, as aforementioned. A significant increase in cost is needed to enhance the performance of such elements in order to enhance the frame-relaying capability, and a CPU of high performance, if employed, will cause a significant increase in cost.